DESCRIPTION (Investigator's Abstract): This project is designed to investigate mechanisms of evolution of sensory systems in the brain, using a blind cave fish Astyanax jordani and its closely related sighted ancester the riverfish Astyanax mexicanus, as well the goldfish, for comparison. The investigator has previously shown that the optic tectum of the cave fish responds to somatic sensory input instead of visual input. In this study the tracer DiI will be used to trace the somatic sensory pathway to the tectum in the cave fish, and related pathways in the riverfish and goldfish. These will consist of defining in turn: 1) the termination of the spinal and trigeminal nerves in the spinal cord and brainstem, 2) the ascending projections from these receptive regions, and 3) projections to the optic tectum. Electrophysiological recording from structures along the identified pathway to the tectum will be used to determine that they do carry appropriate somatic information.